L-MT-23-043, 10 CFR 50.55a(z)(1) Request Regarding OMN-17, Revision 1. VR-09
| ML23317A222 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 11/13/2023 |
| From: | Brown G Northern States Power Company, Minnesota, Xcel Energy |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| L-MT-23-043 | |
| Download: ML23317A222 (8) | |
Text
(},, Xcel Energy*
November 13, 2023 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Monticello Nuclear Generating Plant Docket No. 50-263 Renewed Facility Operating License No. DPR-22 10 CFR 50.55a{z)(1) Request Regarding OMN-17, Revision 1. VR-09 2807 West County Road 75 Monticello, MN 55362 L-MT-23-043 10 CFR 50.55a Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (hereafter NSPM), hereby requests the U.S. Nuclear Regulatory Commission (NRG) authorization of this 10 CFR 50.55a(z)(1) alternative to support the implementation of the Sixth lnservice Testing Ten-Year Interval for the Monticello Nuclear Generating Plant (MNGP).
NSPM requests authorization to adopt two modifications to the.American Society of Mechanical Engineers (ASME) Operations and Maintenance (OM) Code Case OMN-17, Revision 1, "Alternative Rules for Testing ASME Class 1 Pressure Relief/Safety Valves", per the Enclosure.
Summary of Commitments This letter makes no new commitments and no revisions to existing commitments.
If there are any questions or if additional information is required, please contact Mary Emanuelson at (612) 330-5850 or mary.emanuelson@xcelenergy.com.
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C ~wL/J Gregory D. Brown Plant Manager, Monticello Nuclear Generating Plant Northern States Power Company - Minnesota Enclosure cc:
Administrator, Region Ill, USNRC Project Manager, Monticello, USNRC Resident Inspector, Monticello, USNRC
L-MT-23-043 Enclosure
- 1. Project
Title:
NSPM 10 CFR 50.55a Request Associated with the Monticello Sixth lnservice Testing Ten-Year Interval OMN-17, Revision 1 (L-MT-23-043)
- 2. Licensee:
Northern States Power - Minnesota (NSPM)
- 3. Licensee
Contact:
Mary Emanuelson
- 4. Licensee Contact Phone Number:
(612) 330-5850
- 5. Licensee Contact e-mail:
mary.emanuelson@xcelenergy.com
- 6. Request Type:
- 7. lnservice Inspection or lnservice Testing:
lnservice Testing (1ST)
- 8. Document Sensitivity:
Non-Sensitive
- 9. Select Units That Apply for this Submission:
Monticello (05000263)
- 10. Requested Completion Date:
November 30, 2024
- 11. Proposed Alternative Number or Identifier:
L-MT-23-043 Enclosure VR-09
- 12. Brief Description of Proposed Alternative:
NSPM Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (hereafter "NSPM"), hereby requests NRG authorization of this 10 CFR 50.55a(z)(1) alternative to support the implementation of the Sixth lnservice Testing Ten-Year Interval for the Monticello Nuclear Generating Plant (MNGP). Proposed Relief Request VR-09 requests to adopt two modifications to the American Society of Mechanical Engineers (ASME) Operations and Maintenance (OM) Code Case OMN-17, Revision 1, "Alternative Rules for Testing ASME Class 1 Pressure Relief/Safety Valves," as described herein.
Summary of Commitments This submittal makes no new commitments and no revisions to existing commitments.
- 13. Proposed Duration of Alternatives (in terms of ISI/IST Program Interval with Start and End Dates):
This request, upon approval, will be applied to the duration MNGP sixth 1ST ten-year interval that started October 1, 2022 and is scheduled to end May 31, 2032.
- 14. Applicable ASME Code Requirements:
ASME OM Code, 2017 Edition, Division 1, Mandatory Appendix I, "lnservice Testing of Pressure Relief Devices in Water-Cooled Reactor Nuclear Power Plants," paragraph 1-1320, "Test Frequencies," Class 1 Pressure Relief Valves, subparagraph(a) 5-Yr Test Interval, which specifies that:
Class 1 pressure relief valves shall be tested at least once every 5 years, starting with initial electric power generation. No maximum limit is specified for the number of valves to be tested within each interval; however, a minimum of 20% of the valves from each valve group shall be tested within any 24-month interval. This 20% shall consist of valves that have not been tested during the current 5-year interval if they exist. The test interval for any installed valve shall not exceed 5 years. The 5-year test interval shall begin from the date of the as-left set-pressure test for each valve.
ASME OM Code, Operation and Maintenance of Nuclear Power Plants, 2017 Edition with no Addenda.
- 16. Current ISi or 1ST Program Interval Number and Start/End Dates (as Applicable):
MNGP is currently on its sixth 1ST ten-year interval that began on October 1, 2022 and is scheduled to end May 31, 2032.
Page 2 of 7
L-MT-23-043 Enclosure
- 17. Applicable ASME Code Components and/or System
Description:
NSPM The table below provide the list of valves that are within the scope of this 10 CFR 50.55a(z)(1) alternative.
Pressure Relief/Safety Valves-Table 1 Component Description Class Category RV-2-71A Main Steam Line Safety/Relief Valve on 1
BC MSLA RV-2-71 B Main Steam Line Safety/Relief Valve on 1
BC MSL B RV-2-71C Main Steam Line Safety/Relief Valve on 1
BC MSLC RV-2-71 D Main Steam Line Safety/Relief Valve on 1
BC MSL D RV-2-71 E Main Steam Line Safety/Relief Valve on 1
BC MSLA RV-2-71 F Main Steam Line Safety/Relief Valve on 1
BC MSLD RV-2-71 G Main Steam Line Safety/Relief Valve on 1
BC MSL B RV-2-71 H Main Steam Line Safety/Relief Valve on 1
- 18. Reason for Request:
At MNGP, there are eight Target Rock, 3-stage, base Model 67F (Model Nos.73-67F and 74-67F)
Main Steam Safety Relief Valves (MSRVs) installed on the Main Steam lines inside the drywell. All valves have a nominal 1109 psig setpoint. These valves are classified into the same in service testing (1ST) program valve group. In accordance with the requirements of ASME OM Code, Mandatory Appendix I, paragraph 1-1320, subparagraph (a), the installed MSRVs are to be pressure tested within five years from the date of the as-left set-pressure test for each valve. ASME OM Code Case OMN-17, Revision 1, is being utilized to extend the l-1320(a), five-year test interval to six years, along with the potential use of a six-month grace period. MNGP is currently operating on a 24-month refueling cycle. ASME OM Code Case OMN-17, Revision 1, allowed MNGP to go from testing all eight MSRVs over two refueling outages, to testing all eight over three refueling outages. This potentially reduces the number of MSRVs being tested over three refueling outages by two MSRVs. The MNGP MSRVs have had historically good set-pressure performance (as described herein).
An assessment of the MNGP Target Rock MSRVs performance concluded that there is reasonable assurance that each MSRV will retain the set pressure within the required drift tolerances after
L-MT-23-043 Enclosure NSPM extending the test interval to the proposed eight-year test interval. Extending the MSRV test interval from six to eight years reduces the number of valves tested, reducing occupational radiological dose incurred during the MSRV removal, testing, and re-installation maintenance activities.
- 19. Full Description of Proposed Alternative:
NSPM proposes an alternative to the MSRV testing requirements of ASME OM Code, Mandatory Appendix I, section l-1320(a), and ASME Code Case OMN-17, Revision 1. The basis of the request is that MSRV set pressure performance assessment supports the conclusion that the proposed alternatives would provide an acceptable level of quality and safety.
NSPM implemented ASME Code Case OMN-17, Revision 1, in its entirety and requests the following changes: 1) increase the test interval from six to eight years, along with the potential use of ISTA-3170, "lnservice Examination and Testing Frequency Grace," of the OM Code (2017 Edition) which may be utilized to accommodate extended shut down periods, and 2) changes the minimum number of MSRVs tested from 20% to 40-010 in the valve group with a proposed 48-month interval (described further herein). This reduces the number of MSRVs removed and tested over an eight-year interval and will decrease occupational dose.
- 20. Description of Basis for Use:
As an alternative to the ASME OM Code-required five-year test interval per Mandatory Appendix I, paragraph l-1320(a), and the six-year test interval permitted by Code Case OMN-17, Revision 1, NSPM proposes that this 10 CFR 50.55a(z)(1) alternative be granted to allow utilization of ASME Code Case OMN-17, Revision 1, with two modifications, as follows: The first modification proposes that the MS RVs be tested at least once every eight years from the date of the as-left set pressure test for each valve, with a six-month grace period to coincide with the combined certification testing and RFO time periods, for an interval not to exceed 8.5 years. The second modification changes the minimum number of MSRVs from the valve group to be tested from 20% within any 24-month interval, to 40% within any 48-month interval, with the 40% population made up of MSRVs which have not been tested during the current 96-month interval, if they exist. The additional requirements stipulated within ASME Code Case OMN-17, Revision 1, will be retained.
NSPM has incorporated the guidance of 2015 EPRI Technical Report (TR) "Nuclear Maintenance Applications Center: Safety and Relief Valve Testing and Maintenance Guide" Revision of TR 105872, Technical Report 3002005362, into the procedures for receipt inspection requirements, predictive maintenance and inspection of the MS RVs. NSPM recently performed an evaluation of the performance of the Target Rock MSRVs.
Page 4 of 7
L-MT-23-043 Enclosure NSPM It was concluded that there was reasonable assurance that the required setpoint drift tolerance of~
3% would be met after extending the test interval from the current six-year interval to a proposed eight-year interval.
This assessment reviewed as-left/as-found set pressure data going back to 2017 and identified;
- 1) Whether the valves' set pressure drifted up or down, and 2) The absolute set pressure change between tests. Based on the time between the as-left and as-found set pressure test of each MSRV, the set pressure drift was then linearly extrapolated to determine whether the MSRV's set pressure would still be within the site's required~ 3% tolerance band following an eight-year period. Table 2 summarizes the setpoint drift projection, in years of service, predicting when each MSRV would exceed the+/- 3% set pressure tolerance band for MSRVs removed and tested since 2017.
Table 2 also includes as-left testing for setpoint for each MSRV. The NSPM MSRV Precision/Critical Maintenance practices are developed from the application of the EPRI/NMAC Safety and Relief Valve Testing and Maintenance Guide (Reference 2) and from NSPM Operational Experience (OE). The NSPM MSRV Precision/Critical Maintenance has been implemented through NSPM's oversight of the valve vendor's test and rebuild processes.
Table 2 e pom s e s-oun e ormance SRV S t
- t A L ft/A F d P rf p
- f ro1ec 10n As-Left As-Found Pilot SN SRV Main Body Date Pressure Date Pressure Years to+/- 3%
Loe (psig)
(psig) 122 C
217 10/31/2012 1108 4/28/2017 1118 14.8 7
D 216 11/6/2012 1116 4/28/2017 1120 36.9 195 B
1458 1/27/2015 1108 4/26/2019 1108
>50 177 A
4 2/6/2015 1111 4/26/2019 1115 34.8 123 G
25 3/2/2015 1119 4/26/2019 1123 34.3 217 E
123 3/3/2015 1107 4/26/2019 1095 11.4 216 C
122 3/13/2017 1119 4/30/2021 1122 45.5 242*
F 1449 3/13/2017 1111 4/30/2021 1092 7.2 119 H
53 3/14/2017 1117 4/30/2021 1113 34.1 208 D
208 3/14/2017 1101 4/30/2021 1097 34.1 5
B 195 3/18/2019 1104 4/6/2023 1100 33.5 169 E
196 3/20/2019 1106 4/30/2021 1104 34.9 170 G
170 4/3/2019 1106 4/6/2023 1108
>50
L-MT-23-043 Enclosure NSPM
- Topworks disassembled, cleaned, and inspected. The pilot filter, preload spacer, and second stage disc were machined. Seats lapped. Second stage hex nut replaced. All wear and contact areas were polished and lubricated.
No post-repair leakage, pre-or post-test. Lowering setpoint protects from overpressure.
Extending the test interval from six to eight years and revising the intervening outage testing sample size and frequency are acceptable based upon past MSRV performance. The ASME OM Code requires additional valves to be tested if as-found values are outside the acceptable range. For each MSRV tested at MNGP for which the as-found set pressure exceeds the greater of either the plus/minus tolerance limit of the established set-pressure acceptance criteria or+/- 3% of MSRV nameplate set-pressure, two additional MSRVs are tested from the same valve group. If the as-found set-pressure of any of the additional MS RVs tested exceeds the criteria, then all the remaining valves of that same group will be tested.
This proposed relief request will also align with the principles of maintaining radiation dose As Low As Reasonably Achievable (ALARA). Using recent dose measurements over the past four RFOs, the average radiological exposure incurred per MSRV removal and replacement has been approximately 1.375 Rem. Extending the testing interval from six years utilizing OMN-17, Revision 1, to eight years would allow extending the testing of the eight MSRVs from three to four refueling outages, potentially providing a reduction of four MSRV tests over a ten-year interval. This would lower overall radiological exposure and optimize the testing sequence to support plant configuration.
Based on the past performance of the MS RVs at MNGP there is reasonable assurance that the MSRVs will remain within the setpoint tolerance over the proposed eight-year test interval. This proposal maintains an acceptable level of valve operational readiness, reduces occupational radiological exposure, while providing an acceptable level of quality and safety pursuant to 10 CFR 50.55a(z)(1 ).
- 21. Describe Hardship or Unusual Difficulty:
NOT APPLICABLE
- 22. Include Any Additional Information:
NOT USED (No Attachments)
23. Precedents
Safety Evaluation for the Clinton Power Station, Unit No. 1; Dresden Nuclear Power Station, Units 2 and 3; Nine Mile Point Nuclear Station, Unit 2; Peach Bottom Atomic Power Station, Units 2 and 3; and Quad Cities Nuclear Power Station, Units 1 and 2 - Proposed Alternatives to Extend the Safety Relief Valve Testing Interval (EPID L-2020-LLR-0014 through -0018), dated January 14, 2021 (ADAMS Accession Number ML21005A061)
L-MT-23-043 Enclosure NSPM Safety Evaluation for the Limerick Generating Station, Units 1 and 2 - Issuance of Alternative Requests 41-VRR-8 and 41-VRR7 Regarding Certain lnservice Testing Program Requirements for Safety Relief Valves (EPID L-2020-LLR-0043), dated December 10, 2020 (ADAMS Accession Number ML20322A009)
- 24.
References:
- 1.
ASME OM Code Case OMN-17, Revision 1, "Alternative Rules for Testing ASME Class 1 Pressure Relief/Safety Valves."
- 2.
EPRI 2015 Technical Report. Nuclear Maintenance Applications Center: Safety and Relief Valve Testing and Maintenance Guide. Revision of TR-105872, Technical Report 3002005362, August 2015.